Of the seven churches Laodicea gets the biggest rebuke from the Lord. Very little is known of the ancient inhabitants of Laodicea. But because of the Lord's Words to them, much has been assumed. The actual church of Laodicea continued forward well past the age of this written reprimand. Historical writings suggest that Laodicea became a strong center for Christianity. Laodicea was destroyed by an earthquake in 1354, and was never rebuilt. It appears that when Jesus came, and if there were any to be saved that were truly part of the Body they were taken, and all that, remained at Laodicea were corrupted. They continued to play a role in the corrupted attempts to playing church in an age when the Church ought to have been subjective and spiritual rather than objective and materially based.
Jesus is here called "the Amen," "the faithful and true witness," and "the beginning of the creation of God." He knows their works and knowing them intimately He tells them that they are, relative to their faith, their love - their Christianity that they are not cold towards all such things, nor are they hot. And these words are so very poignant - and applicable as we might all look into our hearts and ask: Am I cold...or am I hot? - as a means to discover if we are lukewarm. Then Jesus says, "I would thou wert cold or hot." That's amazing! That God would rather a people be frozen and dead to Him or that they would be on fire OVER being lukewarm.
Why He would prefer they should be "hot" is clear enough; but why would He prefer a state of cold - a state where there was no existence or profession of real faith or love? It's because at least in the case of someone who is cold to God and the things of God...they are honest. And if there was ever one thing that God and Jesus seems to despise is religious hypocrisy, craftiness in God's name, manipulation and deceit. So honesty is one reason why God would perfer cold or hot - but not lukewarmedness. And if someone is being honest before God, they are being more honorable before Him - even if they are cold in their hearts. We can look at the character of Saul of Tarsus, killing Christians and find merit but look to Judas Iscariot who spent three years with the Lord but never really being on fire for him as two good examples of these opposite character traits. Perhaps there is a greater chance of conversion for the honest cold soul before God rather than the religious hypocrite.
Jesus tells the believers at Sardis that there were a few people who had kept themselves free from the general contamination. Simply put, God has always had a remnant throughout scripture - the biblical principle of a remnant existing throughout all of Christian church history as well, "which have not defiled their garments." Because they have not become corrupt, "they shall walk with Me in white." White is the emblem of innocence, and apparently is a reality in heaven. "For they are worthy" meaning deserving, proven, qualified for reward. It is only Christ in us (through faith on His shed blood) that allows us to stand sinless before God. Central to a willingness to let Jesus reign (by the Spirit) must be the characteristics of genuine love, true humility, and choosing to not live lives of flesh and lust.
Now the letter to Philadelphia, a city only 25 miles from Sardis. Here Jesus seems to be reassuring them that they were the heirs to salvation. Whoever looks to Him can walk through the door Christ has opened and "no one can shut it." Christ is the only one who can grant access to God, and Christ has given the Christians at Philadelphia access to God and no one can deprive them of it. Bottom line - Christ is saying that He has the key of David. As a material King David's key opened the door to any who would enter the Nation of Israel. Far more importantly, Jesus now and forever after opens the door for the church or body of believers - which allows all through Him to enter into the presence of God. He IS the door to the kingdom and therefore the only way to salvation.
Those people who claimed to be Jews (but were not, but were actually liars from the synagogue of Satan) were the ones who persecuted the Saints at Philadelphia. He tells them that these persecutors would eventually bow down before the believers (because He will make them) and they will know that Jesus was always on their side. Here Revelation underscores the notion that the Jews are no longer the people of God as a national or ethnic entity, since they have rejected their Messiah.